This invention relates to semiconductor device packages, and in particular to a package requiring a high density of connections from the semiconductor to external leads.
In standard semiconductor device packaging, the semiconductor chip is electrically connected to outside circuitry by means of a lead frame. The lead frame may be thought of as a solid metal picture frame with fingers radiating inward from either two opposing sides or from all four sides toward the geometric center of the frame. Also radiating inward from each of the four corners of the frame is a finger which terminates on a square or rectangular piece of metal, typically referred to as a paddle, which occupies a portion of the geometric center. One major surface of the chip is bonded to the paddle, and contact pads on the opposite surface are electrically coupled to the lead frame fingers by bonding conductive wires to the pads and fingers. The chip and a portion of the lead frame fingers are then encapsulated or molded in a material such as an epoxy or plastic molding compound, and the molded package body and lead frame fingers are cut from the frame. The lead frame fingers are then formed to provide a means of electrically connecting the package to the second level interconnection board, which is typically a printed circuit board. The severed fingers therefore constitute the I/O (Input/Output) leads for the semiconductor chip.
This standard packaging scheme generally has been satisfactory. However, a problem exists where a high density of connections is required between the chip contact pads and the lead frame fingers due to a great number of such contacts and/or smaller than standard chip sizes. In such cases, it is difficult to fabricate the fingers sufficiently close together to accommodate the high density of interconnections. For example, lead frame fingers cannot usually be made with less than a 16 mil pitch (the distance between the center of two adjacent fingers). In order to provide connection to a chip with 50 pads on a chip side having standard dimensions (320 mils), the ends of the fingers can only be brought to within approximately 240 mils of the chip due to the limit on pitch. This tends to cause sagging and shorting of the wires between the pads and fingers.
One solution to the problem of high density I/O connections involves use of multi-level ceramic or glass packages (see, e.g., U.S. Pat. No. 4,498,122 issued to Rainal). While adequate, such packages are fairly expensive. One possible alternative which has been proposed recently is to provide a multi-level lead frame structure for connecting the chip. (See U.S. patent application of Moyer and Scholz, Ser. No. 816,443, filed Jan. 6, 1986.Iadd., now U.S. Pat. No. 4,801,765, .Iaddend.and assigned to the present assignee.) It is desirable to provide a further alternative package for high density connections.
A further problem which exists in many semiconductor packages is inadequate heat removal from the chip during operation. This is more troublesome as chips become more complex and are required to do more functions. It is, therefore, also desirable to provide a semiconductor package with efficient heat dissipation.
It is, therefore, an object of the invention to provide a semiconductor device package with high density I/O lead connections. It is also an object of the invention to provide such a package with maximized heat dissipation.